When you are writing to defend a thesis statement, you must use information from experts in the field. This gives credibility to your ideas and supports your claim. When you take information from an expert, a research project, an interview or other source, you must give credit to that person.
Here is an online site that can help you.
Purdue University Online Writing Lab
You can also use the information from the Diane Hacker book I have. I think that Ms. Pawlusiak might also have a copy to borrow.